Recently, nitride semiconductor laser devices capable of oscillating in blue wavelength region have been receiving much attention. Also there have recently been demands for a nitride semiconductor laser device that has a high output power. To meet these demands, a laser having ridge structure formed by partially etching a p-type contact layer and a part of a p-type cladding layer has been studied so as to achieve single transverse oscillation mode having good FFP (far field pattern) However, the ridge has a very small width, from 1 μm to 2 μm, and it is difficult to form an ohmic electrode having the same width as that of this ridge. To circumvent this difficulty, a p-type ohmic electrode that contacts with a nitride semiconductor only on the top surface of the ridge has been formed, by covering the entire nitride semiconductor except for the end face with an insulation film with only an n-electrode forming surface being left exposed, then forming the electrode that has a roughly determined width on the ridge. Then a pad electrode of 2-layer structure is formed on the p-type ohmic electrode by forming an Au film on an Au or Ni film.
With the nitride semiconductor laser device of the prior art, however, since the insulation film that covers the entire nitride semiconductor except for the end face needs to have a thickness not less than a certain value in order to protect the device, there has been such a problem that an aperture cannot be precisely formed on the top surface of the ridge, and therefore it is difficult to precisely control the width of contact between the p-type ohmic electrode and the p-type contact layer. Thus it has been difficult to manufacture a laser device with minimum variations in the device characteristics.
Also there has been such a problem that heat generated when the laser device is powered causes Au atoms of the pad electrode to gradually diffuse into a layer underneath, resulting in deterioration of the device characteristics. Particularly when mounting a laser device face-down, conspicuous deterioration of the device characteristics occurs since the diffusion of Au is accelerated by heating to a temperature of about 350° C. for the purpose of face-down mount.